Portland Community College | Portland, Oregon

The laboratory portion of this course provides students with the opportunity to develop skills in the operation of plasma systems.  Students will work in teams of two or more to perform and complete laboratory exercises.  Students must be able to communicate clearly, in oral and written form.

Upon completion of the course students should be able to:

• Anticipate how electrical devices function at RF frequencies when analyzing equipment operation.
• Use concepts of Load Matching and effects of Transmission Line Length to operate and perform basic troubleshooting of RF power supplies and load match networks.
• Discuss with a work group how plasma is generated and used in manufacturing processes, and analyze how the plasma controls affect the process.
• Write technical reports on process and equipment tests, diagnoses and maintenance tasks.
• Identify the hazards associated with a plasma system to avoid injury or death when working on or near such equipment.

The course will include instructor delivered lectures and demonstrations stressing key topics in the course. The instructor will introduce the scientific principles of plasmas, discuss plasma processes and highlight the key elements of plasma processing systems. An emphasis will be placed on practical problem solving. In preparation for the lecture portion of the course, students will be expected to complete all reading and homework assignments.  A strong emphasis is placed on students practicing the principals covered in the laboratory experiments.  Students will run experiments, collect and analyze data, and present the results in reports standard for technology industries.

Assessment may include written reports, homework assignments, quizzes and tests, and participation and performance in the laboratory.

• Plasma Science
• Gas Dynamics and Molecular Properties
• The role mean free path plays in determining the excitation mechanism of glow discharges.
• Excitation, ionization, and dissociation.
• Ionization potential, and its relationship to location in the periodic table.
• Elastic and inelastic collisions.
• In a DC plasma: difference between a dark discharge, a Townsend discharge, a self sustaining discharge, and an arc discharge.
• The dominant sources of electrons in each of the above.
• Cascade ionization and its role in a self sustaining discharge.
• Relaxation.
• Self sustaining glow discharge structure in a tube containing flat electrodes. Identify the approximate location of the following:
  • Crook’s dark space
  • Aston dark space
  • Faraday dark space
  • Anode dark space/sheath
  • Negative glow
  • Cathode glow
  • Anode glow
• The  electric potential distribution for the glow discharge above. Identify the cathode fall, and note its approximate voltage change.
• The curves illustrating the positive and negative ion distributions in the glow discharge above. How these relate to the potential distribution.
• The relationship between thermionic emission, the cathode glow, and the Aston dark space.
• What occurs when thermionic emission becomes the dominant source of electrons in a DC plasma system.
• The changes occurring in a DC glow discharge when an electrically isolated wafer is inserted in the discharge.
• Relate AC Discharges to DC discharges
• Why the use of insulating substrates or electrodes forces the use of an RF source for plasma generation.
• The relationship between excitation frequency, charge up time of a insulated substrate and the presence of a continuous discharge.
• Basic RF plasma reactor configuration. Identify the locations of dark space sheaths, and explain the processes responsible for those sheaths.
• Identify the principal frequencies used for RF plasma excitation.
• The electromagnetic spectrum, identifying the relative locations of electric power, x-rays, radar, visible light, infrared light, UV light, and broadcast radio.
• What happens when you operate an RF plasma system with insulated electrodes at a low frequency. 
• At a sufficiently high frequency, insulated electrodes in an RF system acquire a negative bias. This occurs because the electrons in the system have a longer mean free path than positive ions. As the cycles progress, new electrons arrive at the electrodes, but the field changes direction before positive ions can arrive to counteract them. Explain what stops the electrodes from acquiring an infinite negative bias.
• Explain why plasma ignition is a function of which gas you use, pressure, and the frequency of the applied field.
• Identify the parameters that relate to electron production and loss in an RF system.
• Explain the transfer of power to the discharge.
• State the relationship between electrode area and potential in an RF system. Explain why this relationship is so important to sputtering and etching processes.
• Draw a simple RF plasma system with asymmetric electrode areas. Illustrate the corresponding time-average voltage distribution and explain the role of a "blocking capacitor".
• Discuss significant differences between RF and DC glow discharges.
• Identify and explain the role of the key components of any plasma system.
• Discuss the principal types of plasma systems, their characteristics, and the unique aspects of the associated plasma system.
• Describe how plasma is generated and used in the following processes: Etch, CVD, Sputtering, Ion Implantation, Photolithography.
• Demonstrate an understanding of hazards associated with plasma systems and safety practices appropriate to the use and maintenance of RF equipment, toxic and compressed gases, wet chemicals required for parts clean.
• Analyze RF Circuits
• Identify the key components of an RF generator
• Identify the performance criteria of a waveform generator, and those elements that are relevant to RF plasma systems.
• Transmission Lines and Connectors
• Explain why the elaborate measures necessary for RF transmission are not required for common household electrical lines.
• Explain the concept of electrical length.
• Identify the losses that occur in transmission lines.
• Define voltage and current standing wave ratios.
• Explain what is meant by line termination.
• List trouble-shooting procedures for problems that may be associated with cables.
• Measuring Power
• Directional Watt Meters
• Define reflected / forward power ratio.
• Demonstrate the use of conversion charts for reflected / forward power ratio and voltage SWR.
• Explain why impedance matching is necessary.
• Identify the factors contributing to impedance of the load in an RF process.
• Explain the conditions that lead to the presence of a local minimum in impedance as a function of gas pressure.
• Explain the operation network matching circuits
• Explain how plasma excitation enhances the chemical etch process.
• Explain how plasma processing improves anisotropy of the etch process
• Explain the pros and cons of reactive ion etching and  sputter / ion milling processes, specifically with regard to selectivity and  anisotropy.
• Explain the relationship between frequency, anisotropy, selectivity, and particulate contamination.
• Explain the role of DC Bias in etch processing.
• Explain the role of gas pressure in etch processing.
• Explain the relationship between gas flow rates and etch rates
• Define passivation.
• The five steps that are fundamental to plasma etch processes.
  • Transport (diffusion or direction) of gaseous reactants to the surface.
  • Adsorption of the reacting species on to surface sites.
  • Surface chemical reaction between the reactants.
  • Desorption of the reaction gaseous by-products.
  • Diffusion of by-products away from the surface.
• Explain how plasma excitation enhances the chemical deposition process.
• Explain how plasma processing affects step coverage, bread-loafing, void formation.
• Explain the relationship between frequency and film deposition characteristics.
• Explain the role of DC Bias, deposition pressure, gas flow rates.
• List the steps that are fundamental to deposition process (transport, adsorption, surface chemical reaction).
• Identify sources of particulate contamination, list common precautions to minimize them, and explain how they can be observed (bubbles effect).